The prostate is a small gland that surrounds the urethra just anterior to the rectum. In men, especially elderly men, it often develops one or more of hypertrophy, benign cysts and nodules, and/or cancers. Prostate cancers range from slow growing, non-invasive types to highly aggressive, fast growing, and invasive types. As prognosis and treatment for each of these conditions differs, it is desirable to reliably distinguish them.
There are about 230,000 cases of prostate cancer diagnosed in the United States each year, but a large number of cases remain undetected. For example, studies show that needle biopsies miss 40-50% of clinically threatening carcinomas. This high occurrence of false negatives is troublesome because highly effective life-saving measures are available when detection occurs early in the disease.
To improve the odds of detection, several imaging modalities that guide biopsy procedures and/or provide independent diagnostic results have been developed. Transrectal ultrasound (“TRUS”) is one such imaging technique that is typically used to guide biopsy needles. TRUS involves high frequency sound waves in the range of about 1 to 20 MHz. These sound waves are emitted by an ultrasound probe, then travel through tissue until they are reflected by interfaces between different types of tissues, such as between differing organs, between healthy tissue and denser cancerous tissue, or between soft tissue and bone. An ultrasound probe receives reflected sound waves (echoes) and instrumentation calculates distances between the probe and the reflecting boundary, typically displaying an image of detected boundaries. The ultrasound technique provides good (sub-millimeter) spatial resolution and can identify the borders of organs such as the prostate, and possibly can identify borders of tumors within such organs, but it is unable to discriminate between benign versus malignant tissue.
Electrical Impedance Imaging (“EII”), on the other hand, is a medical imaging technique that provides tissue characterization. The technique involves attaching conductive electrodes to a surface of a patient, applying small currents to two or more of the electrodes and measuring electrical potentials at one or more electrodes. From these measurements, electrical impedance of tissue may be determined. The process is repeated for many different configurations of the applied current. Subsequent computation produces a 3D map of the electrical properties of tissues, which correlate with tissue types and pathologies. EII offers low cost, low resolution, images limited by inaccurate modeling of regionally varying electrode-patient contact and poor signal-to-noise contrast.